$ ./perl6 -e 'say 3.isa(Mu:U)'
True
That's not the right answer for what I want Mu:U to do. Actually the
attempt at a definedness constraint is being totally ignored here, as
it also is in "my Mu:U $a" and other places where it's not currently
implemented. Silent ignorance is less than awesome. This should signal
an error, until it's implemented.
-zefram